This article evaluates the progress of the European Union’s Common Foreign and Security Policy (CFSP) following the Lisbon Treaty by conducting a comparative case study of the Kosovo conflict (1999) and the Ukraine crisis (2014). The study first examines the differences between the Lisbon and Maastricht Treaties, then analyzes the characteristics of the two crises, and finally assesses the EU’s foreign policy performance in each context. Findings indicate that the EU’s response to the Ukraine crisis demonstrated greater cohesion and effectiveness compared to the Kosovo conflict. However, despite improvements in coordination and decision-making mechanisms post-Lisbon, challenges persist, particularly regarding the attainment of positive peace. This study highlights the evolving role of the EU as a supranational actor in foreign and security affairs and offers insights into the implications of treaty reforms on the Union’s crisis management capacity.